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QUESTION BANK
SPECIAL ELECTRICAL MACHINES
SEVENTH SEMESTER EEE
TWO MARK QUESTIONS
1.
2.
3.
4.
What is a synchronous reluctance motor?
What are the types of rotor in synchronous reluctance motor?
Mention some applications of synchronous reluctance motor.
What are the advantages of increasing Ld / Lq ratio in synchronous
reluctance motor?
5. Compare Synchronous reluctance motor with induction motor.
6. Write down the torque equation of synchronous reluctance motor.
7. Draw the torque-angle characteristics of synchronous reluctance
motor.
8. Draw the speed-torque characteristics of synchronous reluctance
motor.
9. Draw the steady state phasor diagram of synchronous reluctance
motor.
10. What is a vernier motor?
11. What is the application of vernier motor?
12. Mention some advantages and disadvantages of synchronous
reluctance motor.
13. List out any two properties of synchronous reluctance motor.
14. What do you mean by reluctance torque in synchronous reluctance
motor?
15. Highlight the design considerations in synchronous reluctance motor.
16. Comment on stepper motor.
17. Define the term step angle.
18. Define slewing.
19. Mention the formula for motor speed of stepper motor.
20. Define Resolution.
21. State some applications of stepper motor.
22. Enumerate the advantages and disadvantages of stepper motor.
23. What are different types of stepper motor?
24. What are the different modes of excitation in a stepper motor?
25. What is meant by full-step operation?
26. What is meant by half-step configuration?
27. Sketch the diagram of a VR stepper motor.
28. What is meant by micro stepping in stepper motor?
29. What are the main applications of micro stepping VR stepper motor?
30. What is a multi-stack VR stepper motor?
31. What are advantages and disadvantages of VR stepper motor?
32. What are the advantages and disadvantages of permanent magnet
stepper motor?
33. What is a hybrid stepper motor?
34. What are the advantages and disadvantages of hybrid stepper motor?
35. Draw the typical static characteristics of a stepper motor.
36. Distinguish between VR, PM, and hybrid stepper motor.
37. Define holding and detente torque.
38. Define torque constant.
39. Draw the typical dynamic characteristics of a stepper motor.
40. Differentiate pull-in torque from pull-out torque.
41. Differentiate pull-in rate from pull-out rate.
42. What is a response range?
43. What do you mean by slewing range?
44. What do you mean by synchronism in stepper motor?
45. What do you mean by mid-frequency resonance in stepper motor?
46. Draw the block diagram of the drive system of a stepper motor.
47. What is a logic sequencer?
48. What is meant by power drive circuit in stepper motor?
49. What is the use of current suppression circuit?
50. What are the different types of current suppression circuit?
51. Draw any two drive-circuits for stepper motor.
52. How is step of permanent magnet stepper motor controlled?
53. Mention the types of power controllers used for switched reluctance
motor.
54. Why rotor position sensor is essential for the operation of switched
reluctance motor?
55. List out the drawbacks of switched reluctance motor.
56. Mention the merits of switched reluctance motor.
57. Draw the general speed-torque characteristics of switched reluctance
motor.
58. What are the applications of SRM?
59. What do you mean by switched reluctance motor?
60. Draw the “λ-I” curve for SRM.
61. What are the two types of current control techniques?
62. What do you mean by energy ratio?
63. Draw the simple block diagram of SRM.
64. Draw the circuit of PWM type current control.
65. What do you understand by phase windings?
66. Highlight the essential difference between SRM and stepper motor.
67. Write down the torque equation for a switched reluctance motor
drive.
68. Sketch the C-dump converter circuit for switched reluctance motor.
69. What do you mean by hysteresis current control?
70. Define chopping and single pulse mode of operation of SRM.
71. List down the advantages and disadvantages of brushless dc motor
drives.
72. List the various permanent magnet materials.
73. Draw the magnetic circuit of 2 pole permanent magnet brushless dc
motor.
74. Bring down the differences between mechanical and electronic
commutators?
75. Write the torque and emf equation of square wave brushless dc motor
drive.
76. Mention some applications of PMBLDC motor.
77. Compare conventional dc motor with PMBLDC motor.
78. Why the PMBLDC is motor called as the electronically commutated
motor?
79. What are the classifications of BLPM dc motor?
80. What are two types of BLPM SQW DC motor?
81. Name the position sensors that are used for PMBLDC motor.
82. What are materials that are used for making Hall IC pallet?
83. What are the relative merits of the brushless dc motor drives?
84. Draw the circuit diagram of electronic commutator.
85. Compare PMBLDC motor and switched reluctance motor.
86. Differentiate Hall sensor from optical sensor.
87. What are the types of permanent magnet DC motor?
88. What is permanent magnet DC commutator motor?
89. What are features of permanent magnet synchronous motor?
90. Highlight the advantages of load commutation.
91. Write down the expressions for power input and torque of permanent
magnet synchronous motor.
92. List the applications of permanent magnet synchronous motor.
93.What are features of closed-loop speed control of load commutated
inverter fed synchronous motor drive?
94. What are merits and demerits of permanent magnet synchronous
motor?
95. Write the emf equation of permanent magnet synchronous motor.
96. What are the assumptions made in derivation of emf equation for
permanent magnet synchronous motor?
97. Why PMSM operating in self controlled mode is known
commutatorless dc motor?
98. What do you mean by “pulsed mode” of operation of permanent
magnet synchronous motor?
99. Clearly explain the differences between synchronous reluctance
motor and permanent magnet synchronous motor.
100. Write down the expressions for self and synchronous reactance of
permanent magnet synchronous motor.
101. What do you mean by self control of permanent magnet synchronous
motor?
102. What is meant by field oriented control of permanent magnet
synchronous motor?
103. How are PMBLDC and PMSM different?
104. Draw the phasor diagram of a permanent magnet synchronous motor.
105. State any two classifications of permanent magnet synchronous
motor and its types.
106. Distinguish between self control and vector control of permanent
magnet synchronous motor.
107. What is meant by slotless motor?
16 MARKS QUESTION
1. Explain the principle of operation and constructional features of
synchronous reluctance motor.
2. Explain circle diagram and torque-speed characteristics of synchronous
reluctance motor.
3. Explain the working of vernier motor with neat diagram.
4. Compare the constructional features of axial and radial gap
synchronous reluctance motor.
5. Describe the construction and principle of operation of synchronous
reluctance motor with neat diagrams.
6. Draw and explain the steady sate phasor diagram of synchronous
reluctance motor. What changes will be made if a permanent magnet is
placed on the rotor of same?
7. Explain the different modes of excitation used in variable reluctance
stepper motor?
8. Describe the construction and working principle of hybrid stepping
motor.
9. Write detail about mini step drive.
10. Describe the working of a 3 stack stepper motor having 12 poles in
stator and in rotor.
11. Analyze the mechanism of torque production in VR stepper motors.
12. State and explain static and dynamic characteristics of a stepper motor.
13. Discuss in detail the different types of power drive circuits for stepper
motor.
14. Draw the bi-directional two phase logic sequencer for four phase
stepper motor and draw the truth table and explain its operation.
15. Explain dual voltage drives for a two phase on drive of a four phase
motor with necessary circuit diagrams.
16. Explain the different types of current suppression circuits.
17. A stepper motor driven by a bipolar drive circuit has the following
parameters: winding inductance = 30 mH, rated current = 3A, DC
supply = 45V, total resistance in each phase = 15Ω. When the
transistors are turned off, determine (i) the time taken by the phase
current to decay to zero and (ii) the proportion of the stored inductive
energy returned to the supply.
18. A stepper motor has a step angle of 3 ˚. Determine (a) resolution (b)
number of steps required for the shaft to make 25 revolutions and (c)
shaft speed, if the stepping frequency is 3600 pps.
19. A stepper motor has a step angle of 1.8˚. What number should be
loaded into the encoder of its drive system if it is desired to turn on the
shaft ten complete revolutions?
20. What is the motor torque Tm required to accelerate an initial load of
3*10-4 kg m2 from f1 = 1000 Hz to f2 = 2000 Hz during 100 ms. The
frictional torque Tf is 0.05 N-m and the step angle is 1.8˚.
21. Explain the construction and working principle of SRM.
22. Explain why rotor position sensor is essential for the operation of
SRM.
23. Describe the various power controller circuits applicable to switched
reluctance motor and also explain any one scheme operation with neat
diagrams.
24. Draw the schematic diagram and explain the operation of a ‘C’ dump
converter used for the control of SRM.
25. Discuss the various converter topologies for a 3 phase SR motor with
merits and demerits of each. Explain any two of them.
26. Sketch the general speed-torque curve of SR motor and discuss the
type of control strategy used for different regions of the curve. Sketch
the typical phase current waveforms of low speed operation.
27. Describe the hysterisis type and PWM type current regulator for one
phase of a SRM.
28. Explain the various duty cycle schemes for a phase of three SR motor
and its operation with phase current waveforms.
29. Discuss in detail about microprocessor based control of SRM.
30. Discuss in detail about computer control of SRM.
31. What is the step angle of a 5 phases SRM and commutation frequency
in each phase for the speed of 6000 rpm. SRM is having 10 stator poles
and 4 rotor poles.
32. A SRM with 6 stator poles and 4 rotor poles has a stator pole arc of 30
degree and rotor pole arc of 32 degree. The aligned inductance is 10.7
mH and unaligned inductance is 1.5 mH. Saturation can be neglected.
Calculate the instantaneous torque when the rotor is 30 degree before
the aligned position and phase current is 7A. What is the maximum
energy conversion one stoke, if the current is limited to 7A? Determine
the average torque corresponding to this energy conversion.
33. Sketch the structure of controller for PMBLDC motor and explain the
functions of various blocks.
34. Explain the closed loop control scheme of a permanent magnet
brushless DC motor drive with suitable schematic diagram.
35. Derive the expressions for emf and torque of a PM brushless dc motor.
36. Discuss in detail about the operation of an electronic commutator.
37. Discuss the use of Hall sensors for position sensing in PMBLDC
motors.
38. Compare PMBLDC motor with switched reluctance motor and bring
out its features.
39. A PMBLDC motor has torque constant 0.12 Nm/A referred to DC
supply. Find no load speed when connected to 48V DC supply. Find
stall current and stall torque if armature resistance is 0.15Ω / phase and
drop in controller transistors is 2V.
40. A PMBLDC motor has a no-load speed of 6000 rpm when connected
to a 120 V supply. The armature resistance is 2.5Ω and rotational and
iron losses may be neglected. Determine the speed when the supply
voltage is 60V and the torque is 0.5 Nm.
41. Explain the construction and operation of PMSM.
42. Compare electromagnetic excitation with permanent magnet of a
PMSM.
43. Clearly in detail explain the differences between synchronous
reluctance motor and PMSM.
44. Explain the principle of operation of a sine wave PMSM in detail by
drawing the phasor diagram and also derive the torque equation.
45. Derive the emf equation of PMSM.
46. Derive the expressions for power input and torque of a PMSM. Explain
how its torque-speed characteristics is obtained.
47. Explain in detail the vector control of PMSM.
48. Explain the microprocessor based control of PMSM.
49. A three phase , four pole, brushless PM rotor has 36 stator slots. Each
phase winding is made up of three coils per pole with 20 turns per coil.
The coil span is seven slots. If the fundamental component of magnetic
flux is 1.8 Mwb, Calculate the open circuit phase emf at 3000 rpm.
50. A three phase, 16 poles synchronous motor has a star connected
winding with 144 slots and 10 conductors per slot. The flux per pole is
0.03 wb, sinusoidally distributed and the speed is 375 rpm. Find the
frequency and the phase and line emf. Assume full pitched coil.